POTENTIOMETRIC DISCRIMINATION OF ORGANIC AMINES BY LIQUID MEMBRANE ELECTRODES BASED ON A LONG ALKYL CHAIN DERIVATIVE OF BETA-CYCLODEXTRIN

A long alkyl chain derivative of beta-cyclodextrin yl-6A,6B,6C,6D,6E,6 F,6G-heptatio-beta-cyclodextrin tetradecaacetate) was examined as a ne w type of sensory element of an ion-selective electrode for organic am ines. Poly(vinyl chloride) (PVC) matrix liquid membrane electrodes bas ed on this host were prepared by using several membrane solvents, amon g which 2-fluoro-2'-nitrodiphenyl ether (FNDPE) was found to be by far most effective for potentiometric responses by the cyclodextrin host. Guest-induced potential changes were examined at pH 5.0 for several g roups of protonated organic amine guests having different types of non polar moieties. The magnitude of the guest-induced potential change wa s in the order of 2-phenylethylamine > 1-adamantanamine > benzylamine > cyclohexanamine > dopamine. Potentiometric discrimination was also o bserved for the positional isomers of di- and trimethoxybenzylamines, though the discrimination between the isomers of monomethoxybenzylamin es was negligible. These potentiometric selectivities were quite diffe rent from those for a liquid membrane electrode containing no particul ar sensory element. No appreciable effect was observed by addition of potassium tetrakis (p-chlorophenyl)borate as a fixed anionic site. Suc h a characteristic feature of this cyclodextrin-based liquid membrane electrode was explained in terms of the availability of an inclusion c omplex between the cyclodextrin host and each guest in a geometry that would be stable at the membrane surface.